1. Field of the Invention
The present invention relates to an electrostatic capacitance diaphragm vacuum gauge and a vacuum processing apparatus.
2. Description of the Related Art
An electrostatic capacitance diaphragm vacuum gauge can measure pressures highly accurately and be mass-produced using a micromachine (MEMS) technique, and accordingly it is widely used as a pressure sensor for a vacuum processing apparatus or the like.
The electrostatic capacitance diaphragm vacuum gauge is an apparatus in which a diaphragm and a detection electrode opposing the diaphragm are arranged in a vacuum. This apparatus measures the pressure by measuring the degree of change in the electrostatic capacitance between the diaphragm and the detection electrode.
FIG. 3 is a schematic sectional view showing an electrostatic capacitance diaphragm vacuum gauge disclosed in Japanese Patent Laid-Open No. 2001-255225 as a prior art.
As shown in FIG. 3, in this electrostatic capacitance diaphragm vacuum gauge, a conductive wiring line 4 is formed in an insulating substrate 1 made of glass or the like to extend through it.
The insulating substrate 1 and a conductive substrate 2 bonded to each other in a vacuum atmosphere form a reference pressure space 5 inside them. The reference pressure space 5 forms a vacuum-sealed closed space.
For example, a non evaporable getter 6 which absorbs residual gas is placed in the reference pressure space 5. The interior of the reference pressure space 5 is maintained in a high vacuum.
When a gas pressure acts on a diaphragm 3 through a region 10 communicating with the interior of a vacuum processing apparatus 9, the diaphragm 3 deflects toward a detection electrode 7 in accordance with the difference between the gas pressure and the pressure in the reference pressure space 5.
This increases the electrostatic capacitance between the detection electrode 7 and diaphragm 3. Information on the degree of increase in the electrostatic capacitance is sent to an electrical circuit 12 through the conductive wiring line 4 and an electrode pad 11. The electrical circuit 12 performs signal processing to convert the input information on the degree of change in the electrostatic capacitance into a voltage and amplify it. A signal processed by the electrical circuit 12 is obtained from an electrical output terminal 13 as the internal pressure of the vacuum processing apparatus 9.
A change in environmental temperature or the like mechanically distorts a pressure sensor. Then, the electrostatic capacitance changes and causes a measurement error. A reference electrode 8 is used to compensate this measurement error.
In the conventional electrostatic capacitance diaphragm vacuum gauge, distortion caused by a difference in coefficient of thermal expansion between the insulating substrate 1 and the conductive substrate 2 on which the insulating substrate 1 is bonded is inevitable because of its manufacturing method. The reference pressure space 5 formed by bonding the insulating substrate 1 and conductive substrate 2 is also distorted by the reception of the atmospheric pressure. To solve problems and improve the accuracy of pressure measurement, elimination of an error in pressure measurement caused by these distortions is sought.
The distortion caused by the difference in coefficient of thermal expansion between the insulating substrate 1 and conductive substrate 2 depending on the environmental temperature and the distortion caused by the atmospheric pressure are measurement error factors.
As described above, the existence of the reference electrode 8 compensates the measurement error resulting from the ambient temperature variation among the measurement error factors. To measure pressures more accurately, however, the measurement errors factors caused by the atmospheric pressure's change must be also compensated.